Residual stress measurements and weld characterization in wind turbine support structures

Tensile residual stresses are a byproduct of welding processes with a negative impact on fatigue life and structural integrity. In large welded structures, the residual stress field will be superimposed on the service and structural loads, thus potentiating structural limit conditions. Due to the high manufacturing costs involved and harsh environments in which large length welded joints may operate, it is highly desirable to have an overview of the residual stresses present in the structure.In order to gain further insight on the magnitude and nature of welding residual stresses introduced into tubular steel towers, two specimens that were circumferentially welded were obtained from two towers. The specimens were extracted from door cut-outs that permit access inside the towers. The Contour method was employed for measuring the locked-in residual stress, and in order to characterize the welds, a microstructural analysis was performed, and mechanical properties, such as impact toughness and Vickers hardness, were assessed.